This invention relates to compositions which are molten at low temperatures; and specifically to such compositions which are useful as electrolyte compositions.
A class of molten compositions which is of special interest is the class of fused salt compositions which are molten at low temperature and are useful as electrolytes. Such molten compositions are mixtures of components which are liquid at temperatures below the individual melting points of the components. The mixtures can form molten compositions simultaneously upon contacting the components together, or after heating and subsequent cooling.
The fused salt compositions are useful as electrolytes in batteries, photoelectrochemical cells, electrorefining and electroplating. Examples of low temperature molten fused salts are the chloroaluminate salts discussed by Wilkes, J. S., et al; in J. Inorg. Chem., Vol 21, 1263-1264, 1982. Alkyl imidazolium or pyridinium salts are mixed with aluminum trichloride (AlCl.sub.3) to form the fused chloroaluminate salts. Also chlorogallate salts made from gallium trichloride and methylethylimidazolium chloride are discussed in Wicelinski et al, "Low Temperature Chlorogallate Molten Salt Systems," J. Electrochemical Soc., Vol. 134, 262-263, 1987. The use of the fused salts of 1-alkylpyridinium chloride and aluminum trichloride as electrolytes is discussed in U.S. Pat. No. 4,122,245. Other patents which discuss the use of fused salts from aluminum trichloride and alkylimidazolium halides as electrolytes are U.S. Pat. Nos. 4,463,071; 4,463,072 and Great Britain patent application GB No. 2,150,740A. Unfortunately, the alkylimidazolium salts are difficult to prepare, and the alkyl pyridinium salts are too easily reduced in an electrochemical cell system.
In view of the disadvantages of known compositions, it would be desirable to have fused salt compositions which would not be difficult to prepare and which would be useful as electrolytes in electrochemical cells.